(In,Ga,Al)N optoelectronic devices grown on relaxed (In,Ga,Al)N-on-GaN base layers

1. A method of fabricating a heterostructure device, comprising: (a) obtaining a first layer or substrate; (b) forming a second layer that is at least partially relaxed, comprising: growing the second layer on the first layer or substrate as a coherently strained second layer, within critical thickness limits for the second layer and etching the coherently strained second layer into segments having up to a 1000 micrometer width, or growing a plurality of relaxed III-nitride pillars on the first layer or substrate comprising a Gallium Nitride (GaN) layer, wherein: the relaxed III-nitride pillars include Indium or Gallium, or Indium and Gallium, and the relaxed III-nitride pillars are selectively seeded on the GaN layer and have a width up to 1000 micrometers; wherein: (1) the first layer and the second layer have the same lattice structure but different lattice constants, (2) the first layer and the second layer form a heterojunction, and (3) the heterojunction forms an active area of a device or serves as a pseudo-substrate for the device; and (c) continuing growth of, or re-growing the second layer, wherein the segments are merged or coalesced.

2. The method of claim 1 , wherein the first layer is GaN and the second layer is a nitride containing Indium, Gallium, or Indium and Gallium.

3. The method of claim 1 , further comprising: repeating the steps (a)-(c) using the re-grown or coalesced second layer as the first layer in (a), wherein the segments comprise stripes; changing an orientation of the stripes of the layers in the subsequently deposited heterojunctions to obtain the 2-dimensional relaxation; and gradually increasing or decreasing the lattice constants of the layers in the subsequently deposited heterojunctions.

4. The method of claim 1 , further comprising coalescing the segments with a coherently strained coalescence layer, wherein the coalescing is initiated by raising a temperature above a temperature used to grow the coherently strained coalescence layer prior to continuing the growth of the second layer.

5. The method of claim 1 , further comprising: depositing mask material at a bottom or at a bottom and on a top of the segments to promote coalescence of the segments, and after the segments are merged, continuing growth of the second layer to overgrow masked areas masked by the mask material, thereby forming a continuous at least partially relaxed second layer, or interrupting the growth, removing the mask material on the top of the segments, and continuing the growth of the second layer afterwards.

6. The method of claim 1 , wherein: the etching further comprises: etching the coherently strained second layer into a pattern of stripes resulting in at least partial relaxation of the coherently strained second layer into at least partially relaxed stripes having up to a 1000 micrometer width; and the re-growing of the second layer comprises: (i) growing a GaN coalescence layer under one dimensional (1D) tensile strain on top of the stripe pattern, adopting an a-lattice constant of the stripes in the stripe pattern, and (ii) growing an InGaN layer on the GaN coalescence layer, wherein the InGaN layer adopts the a-lattice constant of the stripes and results in 1D relaxation of the InGaN layer.

7. The method of claim 6 , further comprising patterning the InGaN layer into stripes with an angle between 30 and 90 degrees with respect to the stripes in the second layer, resulting in full or partial two dimensional relaxation of the InGaN layer.

8. The method of claim 1 , further comprising: growing the second layer as a coherently strained InGaN second layer, within critical thickness limits for the second layer, on the first layer comprising GaN; and forming the second layer, comprising: etching the coherently strained second layer into a pattern of first stripes resulting in at least partial relaxation of the coherently strained second layer into at least partially relaxed stripes having up to a 1000 micrometer width; and growing a first coalescence layer having a thickness of 20 nm or less and a different composition to the second layer, on top of the pattern of the first stripes; patterning the first coalescence layer and the second layer into a pattern of second stripes with an angle between 30 and 90 degrees with respect to the first stripes in the second layer, resulting in formation of posts in the second layer and full or partial two dimensional relaxation of the second layer; coalescing the second stripes with a second coalescence layer having a thickness of 20 nm or less; and growing an InGaN layer on the second coalescence layer, wherein the InGaN layer adopts the lattice constant of the posts and has a different material composition to the second coalescence layer.

9. The method of claim 1 , further comprising: growing the second layer as a coherently strained second layer, within critical thickness limits for the second layer, and forming the second layer, comprising: etching the coherently strained second layer into a pattern of the segments resulting in at least 1-dimensional or 2-dimensional partial relaxation of the coherently strained second layer into at least partially relaxed segments having up to a 1000 micrometer width; and the continuing growth of, or the re-growing of, the second layer, wherein the segments are merged or coalesced.

10. The method of claim 1 , further comprising: growing the second layer comprising a coherently strained second layer, within critical thickness limits for the second layer, and forming the second layer, comprising: etching the coherently strained second layer into the segments resulting in at least partial relaxation of the coherently strained second layer into at least partially relaxed segments having up to a 1000 micrometer width; and merging the segments by growing a coalescence layer composed of a material with a different composition than the coherently strained second layer.

11. The method of claim 1 , wherein: the first layer comprises a Gallium Nitride layer, the growing and the forming of the second layer comprises: depositing a mask material on the Gallium Nitride layer, wherein the mask material includes openings having a width up to 1000 micrometers; and growing and forming the second layer comprising the relaxed III-nitride pillar in each of a plurality of the openings, to form a plurality of the III-nitride pillars, wherein the relaxed III-nitride pillars include Indium or Gallium, or Indium and Gallium; and the continuing growth of the III-nitride pillars includes the III-nitride pillars overgrowing the openings to form the relaxed III-nitride film including Indium and/or Gallium.

12. The method of claim 1 , further comprising: growing the second layer comprising an InGaN bulk base layer; growing an InGaN active region coherently on or above the InGaN bulk base layer, wherein: (i) a thickness and Indium composition of the InGaN active region are larger than a thickness and Indium composition of an InGaN active region that is not grown on the InGaN bulk base layer, and (ii) the InGaN bulk base layer: (a) is at least partially relaxed, and (b) has one or more lattice constants that match one or more lattice constants of the InGaN active region grown on the InGaN bulk base layer.

13. The method of claim 1 , further comprising: growing the second layer comprising an n-type InGaN bulk base layer deposited on the first layer comprising a GaN substrate; and growing an InGaN active region coherently on or above the InGaN bulk base layer, wherein: (i) a thickness and Indium composition of the active region are larger than a thickness and Indium composition of an InGaN active region that is not grown on the InGaN bulk base layer, and (ii) the InGaN bulk base layer: (a) is at least partially relaxed, and (b) has one or more lattice constants that match one or more lattice constants of the InGaN active region grown on the InGaN bulk base layer, and (c) a p-type InGaN layer deposited on or above the InGaN active region.

14. The method of claim 13 , further comprising: patterning the InGaN on the GaN substrate; and relaxed InGaN on the patterned InGaN, wherein the InGaN bulk base layer comprises the relaxed InGaN and the active region is deposited on the relaxed InGaN.

15. The method of claim 1 , wherein the second layer comprises one or more quantum wells.

16. The method of claim 1 , wherein the first layer is GaN and the second layer is a nitride containing Aluminum, Gallium, or Aluminum and Gallium.

17. The method of claim 16 , further comprising repeating the steps (a)-(c) using the re-grown or coalesced second layer as the first layer in (a) and gradually decreasing or stepping down the lattice constants of the layers in the subsequently deposited heterojunctions.

18. A method of fabricating a heterostructure, comprising: (a) obtaining a first layer or substrate comprising a III-nitride or GaN base layer; (b) growing a second layer, comprising: (i) (1) depositing a strained In x Ga 1-x N layer on top of the III-nitride or GaN base layer or (2) depositing a strained In x Ga 1-x N layer in nano or micron sized or width openings formed on a surface of the GaN or III-nitride base layer; and (ii) depositing an In y Ga 1-y N layer on the In x Ga 1-x N layer to form a two layer stack, wherein the In y Ga 1-y N layer is thicker than the In x Ga 1-x N layer and y<x, (iii) optionally further comprising, when the strained In x Ga 1-x N layer is deposited using (1), (3) etching the two layer stack with a pattern to form etched features; and (c) selectively etching the thinner In x Ga 1-x N layer, undercutting the thicker In y Ga 1-y N layer in such a way that only a post remains, wherein the thicker In y Ga 1-y N layer is detached from the base layer so that it can relax and adopt its unstrained lattice constant; and (d) growing an In x Ga 1-x N layer on top of the In y Ga 1-y N layer; wherein (1) the first layer and the second layer have the same lattice structure but different lattice constants, (2) the first layer and the second layer form a heterojunction, and (3) the heterojunction forms an active area of a device or serves as a pseudo-substrate for the device.

19. The method of claim 18 , wherein the pattern comprises first stripes oriented in a first direction, the method further comprising repeating steps (a)-(d) wherein: the In x Ga 1-x N layer is the base layer for the next step (a); the strained In x Ga 1-x N layer in the next step (b) is an In s Ga 1-s N layer, the thicker In y Ga 1-y N layer in the next step (b) is a In t Ga 1-t N layer with s>t such that the In s Ga 1-s N layer and the In t Ga 1-t N layer form a coherently strained stack; the etching in the next step (3) is with the pattern comprising second stripes oriented in a second direction; the In z Ga 1-z N layer in the next growing step (d) is fully relaxed for y=t=z or partially relaxed in the presence of small differences between y, t, and z; and x, y, z, t are compositions of Indium in the InGaN layers.

20. The method of claim 18 , wherein adjacent In Y Ga 1-y N features in the stacks are merged by growth of the In z Ga 1-z N, leading to a relaxed (z=y) or partially relaxed (z≠y) In z Ga 1-z N film with a lattice constant corresponding to the patterned relaxed In y Ga 1-y N features.

21. The method of claim 18 , further comprising depositing the strained In x Ga 1-x N layer only in the nano or micron sized or width openings and/or selectively etching the thinner In x Ga 1-x N layer only.

22. An optoelectronic or electronic device, comprising: a second layer comprising an InGaN bulk base layer grown from a first layer or substrate, wherein: (1) the first layer and the second layer have the same lattice structure but different lattice constants, (2) the first layer and the second layer form a heterojunction, (3) the heterojunction forms an active area of a device or serves as a pseudo-substrate for the device; and an InGaN active region coherently on or above the InGaN bulk base layer, wherein: (i) a thickness and Indium composition of the InGaN active region are larger than a thickness and Indium composition of an InGaN active region that is not grown on the InGaN bulk base layer, and (ii) the InGaN bulk base layer: (a) is at least partially relaxed, and (b) has one or more lattice constants that match one or more lattice constants of the InGaN active region grown on the InGaN bulk base layer.

23. The optoelectronic or electronic device of claim 22 , further comprising a device structure grown on the InGaN bulk base layer, wherein: the device structure includes the InGaN active region having the Indium composition of at least 25%, and the InGaN bulk base layer is defect free, has a planar surface, and an Indium composition of at least 25%.